Magnetic Tunnel Junction Memory Device

ABSTRACT

A magnetic-assist, spin-torque transfer magnetic tunnel junction device and a method for performing a magnetic-assist, spin-torque-transfer write to the device are disclosed. In an exemplary embodiment, the magnetic tunnel junction device includes a first electrode, a pinned layer disposed on the first electrode, a free layer disposed on the pinned layer, and a barrier layer disposed between the pinned layer and the free layer. The device further includes a second electrode electrically coupled to the free layer, the second electrode containing a magnetic assist region. In some embodiments, the magnetic assist region is configured to produce a net magnetic field when supplied with a write current. The net magnetic field is aligned to assist a spin-torque transfer of the write current on the free layer.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. In the course of IC evolution, functional density (i.e., thenumber of interconnected devices per chip area) has generally increasedwhile geometry size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling downprocess generally provides benefits by increasing production efficiencyand lowering associated costs. While this process is not without limits,expectations exist of uninterrupted improvement in device scaling,performance, and efficiency. To meet these expectations, newtechnologies must be aggressively pursued.

Magnetic random access memory (MRAM) is an emerging technology fortemporary storage and retrieval of data. Unlike other types of magneticstorage that directly measure magnetic field strength, MRAM data valuesare determined based on the resistance of a magnetic tunnel junction(MTJ) device within an MRAM cell. The MTJ structure typically comprisestwo magnetic layers separated by a thin insulator layer. Data is writtenby altering the magnetic field direction of one of the magnetic layers.This affects the resistance of the structure, thereby storing thewritten data. Although existing MRAM designs have been generallyadequate, they have not proved entirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a simplified perspective view of a magnetic tunnel junction(MTJ) device according to various aspects of the present disclosure.

FIG. 2 is an annotated sectional view of a magnetic tunnel junctiondevice in a first operating condition according to various aspects ofthe present disclosure.

FIG. 3 is an annotated sectional view of a magnetic tunnel junctiondevice in a second operating condition according to various aspects ofthe present disclosure.

FIG. 4 is a perspective view of a spin-torque transfer magnetic tunneljunction device incorporating a partially circular magnetic assistregion according to various aspects of the present disclosure.

FIG. 5 is a perspective view of a spin-torque transfer magnetic tunneljunction device 500 incorporating a piecewise linear, partiallycircular, magnetic assist region according to various aspects of thepresent disclosure.

FIG. 6 is a perspective view of a spin-torque transfer magnetic tunneljunction device incorporating a partially rectangular magnetic assistregion according to various aspects of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates generally to magnetic random accessmemory (MRAM) and more particularly, to a magnetic tunnel junction (MTJ)structure incorporating a magnetic assist feature that utilizes bothspin-torque transfer and a magnetic field to perform a write.

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

A magnetic tunnel junction device (MTJ) is described with reference toFIGS. 1-3. The structure of the magnetic tunnel junction device 100 isdescribed with reference made to FIG. 1. Subsequently, the function ofthe MTJ device 100 is described in further detail with reference made toFIGS. 2 and 3. FIG. 1 is a perspective view of the magnetic tunneljunction (MTJ) device 100 according to various aspects of the presentdisclosure. FIG. 1 has been simplified for clarity. For example, themagnetic tunnel junction device 100 may include one or more dielectriclayers insulting the components of the device 100 and providingstructural support for the device 100 and associated components. Asanother example, the magnetic tunnel junction device 100 may include oneor more passivation layers and/or moisture blocking layers. These havebeen omitted from FIG. 1 to reveal other elements of the device 100 moreclearly.

The magnetic tunnel junction device 100 may be formed on a substrate102, for example, a bulk silicon substrate. Alternatively, the substrate102 may comprise an elementary semiconductor, such as silicon orgermanium in a crystalline structure; a compound semiconductor, such assilicon germanium, silicon carbide, gallium arsenic, gallium phosphide,indium phosphide, indium arsenide, and/or indium antimonide; orcombinations thereof. Possible substrates 102 also include asilicon-on-insulator (SOI) substrate. SOI substrates are fabricatedusing separation by implantation of oxygen (SIMOX), wafer bonding,and/or other suitable methods.

Some exemplary substrates 102 include an insulator layer. The insulatorlayer comprises any suitable material, including silicon oxide,sapphire, other suitable insulating materials, and/or combinationsthereof. An exemplary insulator layer may be a buried oxide layer (BOX).The insulator is formed by any suitable process, such as implantation(e.g., SIMOX), oxidation, deposition, and/or other suitable process. Insome exemplary substrates 102, the insulator layer is a component (e.g.,layer) of a silicon-on-insulator substrate.

The substrate 102 may include various doped regions depending on designrequirements as known in the art (e.g., p-type wells or n-type wells).The doped regions are doped with p-type dopants, such as boron or BF₂;n-type dopants, such as phosphorus or arsenic; or combinations thereof.The doped regions may be formed directly on the substrate 102, in aP-well structure, in an N-well structure, in a dual-well structure, orusing a raised structure. The semiconductor substrate 102 may furtherinclude various active regions, such as regions configured for an N-typemetal-oxide-semiconductor transistor device and regions configured for aP-type metal-oxide-semiconductor transistor device.

The magnetic tunnel junction device 100 may include a first electrode(or bottom electrode) 104 formed on the substrate 102. The bottomelectrode 104 includes a conductive material such as tantalum, platinum,ruthenium, copper, aluminum, titanium, tungsten, molybdenum, tantalumnitride, nickel silicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN,TaC, TaSiN, metal alloys, other suitable materials, and/or combinationsthereof. In an exemplary embodiment, the electrode 104 is formed using aphysical vapor deposition (PVD) process such as sputtering.

In some embodiments, a pinning layer 106 is formed on the bottomelectrode 104, and may be electrically coupled to the bottom electrode104. The pinning layer 106 may include an anti-ferromagnetic material.In anti-ferromagnetic materials, internal magnetic moments tend to alignin alternating patterns. In this configuration, adjacent moments tend tocancel, and thus such materials tend to exhibit a minimal net magneticfield internally. Despite the minimal net field, anti-ferromagneticmaterials may alter the behavior of magnetic fields of other materialsin what is referred to as an exchange coupling effect. For example, ananti-ferromagnetic material may resist changes in the magnetic field ofanother exchange-coupled material. Anti-ferromagnetic materials includeplatinum manganese (PtMn), iridium manganese (“IrMn”), rhodium manganese(“RhMn”), and iron manganese (“FeMn”). The pinning layer 106 may beformed by a suitable deposition technique, such as a PVD process. In arange of exemplary embodiments, an anti-ferromagnetic pinning layer 106is formed to a thickness ranging between approximately 100 angstroms andapproximately 200 angstroms and is formed by a suitable process such asPVD.

A first magnetic layer, referred to as a pinned layer 108, is formed onthe electrode 104. In embodiments incorporating a pinning layer 106, thepinned layer is formed on top of the pinning layer 106. The pinned layer108 may include a ferromagnetic material, for example a cobalt-iron film(CoFe) and/or a cobalt-iron-boron (CoFeB) film. The pinned layer 108 mayalso include other ferromagnetic materials, such as CoFeTa, NiFe, CoFe,CoPt, CoPd, FePt, and/or alloys of Ni, Co and Fe. In some embodiments,the pinned layer 108 has a thickness between approximately 40 andapproximately 60 angstroms.

In some embodiments, the pinned layer 108 includes a multilayerstructure, for example, one or more layers containing a ferromagneticmaterial interspersed with one or more spacer layers containing ananti-ferromagnetic material such as a synthetic anti-ferromagnetic (SAF)material. In one such embodiment, the pinned layer 108 includes twoferromagnetic films interposed by an anti-ferromagnetic spacer layer. Ina further example of a multilayer structure, the pinned layer 108includes one or more layers containing a ferromagnetic materialinterspersed with one or more spacer layers containing a conductivematerial. In one such embodiment, a spacer layer includes Ru. Spacerlayers may include other suitable conductive materials, such as Ti, Ta,Cu, and/or Ag. In layered embodiments, the layers of the pinned layer108 including the ferromagnetic-material containing layers and thespacer layers may be on the order of approximately 5 to approximately 10angstroms in thickness. The ferromagnetic materials, theanti-ferromagnetic materials, and/or the conductive materials that makeup the pinned layer 108 may be applied and formed using a PVD or othersuitable process.

A barrier layer 110 may be formed on the pinned layer 108. The barrierlayer 110 may include a non-magnetic material, such as magnesium (Mg).In various illustrative embodiments, the barrier layer 110 includesmagnesium oxide (MgO), Al₂O₃, aluminum nitride (AlN), aluminumoxynitride (AlON), and/or other suitable non-magnetic material.Exemplary barrier layers 110 have a thickness ranging betweenapproximately 5 and approximately 15 angstroms. The materials of thebarrier layer 110 may be applied by a process including a PVD and/orother suitable deposition process. In one embodiment, a magnesium targetand an oxygen gas are provided in a sputtering chamber to form magnesiumoxide. In another embodiment, a magnesium film is formed by sputtering.The Mg film is then converted into an MgO film by applying an oxygengas.

In some embodiments, the barrier layer 110 has a multilayer structure.For example, in one such embodiment, the barrier layer 110 includes afirst film of MgO and a second film of Mg over the first film. Such astructure may be formed by Mg deposition followed by Mg oxidation andsubsequent Mg deposition. For example, a first magnesium film is formedby sputtering. The first film is then converted into an MgO film byapplying an oxygen plasma. Subsequently, a second Mg layer is depositedon the MgO layer by sputtering. This forms the exemplary MgO/Mg layeredbarrier 110.

A second magnetic layer, the free layer 112, may be formed on thebarrier layer 110. As with the pinned layer 108, the free layer 112 mayinclude a ferromagnetic material such as a cobalt-iron compound (CoFe)and/or a cobalt-iron-boron (CoFeB) compound. In one set of examples,suitable CoFeB compounds have compositions expressed as(Co_(x)Fe_(1-x))₈₀B₂₀, where the subscripts represent alloy molefractions and where x ranges between 0 and 100, inclusive. The freelayer 112 may also include other ferromagnetic materials, such asCoFeTa, NiFe, CoFe, CoPt, CoPd, FePt, and/or alloys of Ni, Co and Fe. Atypical free layer 112 may be between approximately 10 and approximately20 angstroms thick, and deposited using a PVD or other suitable process.

A second electrode (or top electrode) 114 may be formed on the freelayer 112 such that the top electrode 114 is electrically coupled to thefree layer 112. The top electrode 114 may be similar to the bottomelectrode 104 in terms of composition and deposition. For example, theelectrode 114 may include a conductive material such as tantalum,platinum, ruthenium, copper, aluminum, titanium, tungsten, molybdenum,tantalum nitride, nickel silicide, cobalt silicide, TiN, WN, TiAl,TiAlN, TaCN, TaC, TaSiN, metal alloys, other suitable materials, and/orcombinations thereof. In an exemplary embodiment, the electrode 114 isformed using a physical vapor deposition (PVD) process such assputtering.

In the illustrated embodiment, the pinning layer 106, the pinned layer108, the barrier layer 110, and the free layer 112 are approximatelycylindrical, resulting in a device 100 with an approximately cylindricaldevice body 116. In further embodiments, one or more of the layers havean alternate form, for example, a cuboid or an n-sided prism, resultingin a device body 116 with an alternate form. Such embodiments fallwithin the scope of the present disclosure. For ease of reference, alongitudinal axis 118 of the device body is defined extending throughthe pinned layer 108, the barrier layer 110, and the free layer 112.

The function of the magnetic tunnel junction device 100 will now bedescribed with reference made to FIGS. 2 and 3. FIG. 2 is an annotatedsectional view of a magnetic tunnel junction device 100 in a firstoperating condition according to various aspects of the presentdisclosure. FIG. 3 is an annotated sectional view of a magnetic tunneljunction device in a second operating condition according to variousaspects of the present disclosure. Various elements of the magnetictunnel junction device 100 have been omitted from FIGS. 2 and 3 in orderto illustrate other elements more clearly. In many regards, the magnetictunnel junction devices of FIGS. 2 and 3 are substantially similar tothe device 100 of FIG. 1. In that regard the devices of FIGS. 2 and 3may include a bottom electrode 104, a pinning layer 106, a pinned layer108, a barrier layer 110, a free layer 112, and a top electrode 114.

Referring to FIG. 2, the pinned layer 108 exhibits a magnetic field in afirst orientation represented by arrow 202. Thus, the first orientationis substantially perpendicular to the interface of the pinned layer 108and the barrier layer 110 and is substantially parallel to thelongitudinal axis 118 of the device body 116. However, other alignmentsare contemplated and provided for. For example, in some embodiments, thefirst orientation is substantially parallel to the interface of thepinned layer 108 and the barrier layer 110. In some embodiments, thefirst orientation is substantially perpendicular to the longitudinalaxis 118 of the device body 116. These alternative alignments areequally suitable.

In many embodiments, the materials and structure of the pinned layer 108are configured to produce and retain the magnetic field. The field maybe further maintained in part by the pinning layer 106. For example, inanti-ferromagnetic materials commonly used to construct the pinninglayer 106, the magnetic moments of the atoms or molecules align in apattern such that adjacent moments are opposite. As a result, thepinning layer 106 exhibits a minimal net magnetic field internally yethas an exchange coupling effect externally. The exchange coupling raisesthe energy required to reorient a magnetic field of a coupled material,and thus, the anti-ferromagnetic material can be used to “pin” orprevent the switching of the magnetic alignment of the pinned layer 108.It is understood that anti-ferromagnetism is only one example of amethod of pinning the pinned layer 108. Other embodiments incorporateother pinning methods and structures in addition to or as a replacementfor an anti-ferromagnetic pinning layer 106.

In the first operating condition, the free layer 112 also exhibits amagnetic field. The magnetic field orientation, indicated by arrow 204,is substantially parallel to and in substantially the same direction asthe magnetic field orientation of the pinned layer 108. In thiscondition, the alignments of the fields of the free layer 112 and thepinned layer 108 promotes the tunneling of electrons through the barrierlayer. Accordingly, in the first operating condition, the magnetictunnel junction device 100 exhibits a relatively low resistance alongthe body 116 as measured between the top electrode 114 and the bottomelectrode 104.

Referring to FIG. 3, the magnetic tunnel junction device 100 in thesecond operating condition is substantially similar to the device 100 inthe first operating condition. For example, in the embodiment of FIG. 3,the magnetic field of the pinned layer has a first orientation (e.g.,the orientation represented by arrow 202, substantially parallel to thelongitudinal axis 118 of the device body 116). However, the magneticfield of the free layer 112, indicated by arrow 304, is substantiallyparallel to but substantially opposite the field orientation of thepinned layer 108. As a result, the magnetic tunnel junction device 100exhibits a relatively higher resistance along the body 116 as measuredbetween the top electrode 114 and the bottom electrode 104. In anexemplary embodiment, the high resistance is twice the low resistance ofa given device 100. The difference between the low resistance of FIG. 2and the high resistance of FIG. 3 may be expressed as amagnetoresistance ratio. Higher ratios may result in improved readaccuracy, access speed, and device reliability.

The first and second operating conditions may correlate with first andsecond stored data values. For example, the first operating conditionand low resistance state may correspond to a stored “0” binary value,and the second operating condition and high resistance state maycorrespond to a stored “1” binary value. In order to read the storedvalue, an electric potential may be applied between the top electrode114 and the bottom electrode 104, and the device 100 resistance may bemeasured.

Writing stored data involves changing the magnetic field of the freelayer 112 such that the device 100 transitions between a low-resistanceoperating state and a high-resistance operating state and vice-versa. Insome embodiments, a magnetic field is applied to the free layer 112. Amagnetic field of sufficient strength can cause the magnetic momentswithin the free layer 112 to align in either a low-resistance operatingstate orientation (e.g., an orientation substantially parallel to and insubstantially the same direction as the magnetic orientation of thepinned layer 108), or a high-resistance operating state orientation(e.g., an orientation substantially parallel to but substantiallyopposite to the magnetic orientation of the pinned layer 108). A typicalmagnetic field used to write to a device 100 may be betweenapproximately 100 and approximately 150 Gauss. As will be recognized byone of skill in the art, the magnetic field shape and strength may beselected to be sufficient to cause the intended alignment of the freelayer 112 without affecting either the pinned layers 108 or the freelayers 112 of adjacent devices 100. Protecting the adjacent devices 100may involve shielding between devices 100, reduced write field strength,and/or increased spacing between devices 100.

In some embodiments, an electrical current is used to alter theorientation of the magnetic field of the free layer 112. One techniquefor doing so is referred to as spin-torque transfer. Current flowthrough a first ferromagnetic layer, for example, the pinned layer 108,may align the flowing electrons creating a spin-polarized current. Thespin-polarized current can, in turn, transfer the angular momentum ofthe flowing electrons to a second ferromagnetic layer, for example, thefree layer 112. The direction of the current determines whether theinduced magnetic alignment within the second ferromagnetic layer issubstantially parallel to and in substantially the same direction as themagnetic orientation of the first layer or substantially parallel to andsubstantially opposite the magnetic orientation of the first layer. Oneadvantage to spin-torque transfer devices 100 is that the write currentoften lacks sufficient electromagnetic flux to affect neighboringdevices. This may allow spin-torque transfer devices to be spaced closerthan magnetic-field-write devices.

FIG. 4 is a perspective view of a spin-torque transfer magnetic tunneljunction device 400 incorporating a partially circular magnetic assistregion 402 according to various aspects of the present disclosure. FIG.4 has been simplified for clarity. For example, the magnetic tunneljunction device 400 may include one or more dielectric layers insultingthe components of the device 400 and providing structural support forthe device 400 and associated components. As another example, themagnetic tunnel junction device 400 may include one or more passivationlayers and/or moisture blocking layers. These have been omitted fromFIG. 4 to reveal other elements of the device 400 more clearly. In manyregards, the device 400 of FIG. 4 is substantially similar to themagnetic tunnel junction device 100 of FIG. 1. For example, device 400may include a substrate 102, a top electrode 114, a bottom electrode, apinning layer 106, a pinned layer 108, a barrier layer 110, and/or afree layer 112 substantially similar to those of device 100.

In some embodiments, the top electrode 114 includes a magnetic assistregion 402 disposed above the free layer 112. In the illustratedembodiment, the magnetic assist region 402 includes a partially circularcoil region having a winding orientation substantially perpendicular tothe longitudinal axis of the device body 118 (axis omitted for clarity).The magnetic assist region 402 is configured such that current flowthrough the region 402 produces a magnetic field that assists thespin-torque transfer of the current in aligning the magnetic orientationof the free layer 112. In more detail, the write current flowing in afirst direction indicated by arrows 404 exerts a spin-torque tendingtowards establishing a magnetic field in the free layer 112 in thedirection indicated by arrow 204 (e.g., an orientation substantiallyparallel to and in substantially the same direction as the magneticorientation of the pinned layer 108). The same write current flowingthrough the magnetic assist region 402 also produces a net magneticfield as indicated by arrows 406. This net magnetic field alsocontributes to induce, via a magnetic-field write, a magnetic field inthe free layer 112 in the direction indicated by arrow 204 (e.g., anorientation substantially parallel to and in substantially the samedirection as the magnetic orientation of the pinned layer 108). The netmagnetic field induced by a semicircular wire can be calculated by theequation:

H=1/2[μ_(o)*1/2R]

where H is the magnetic field strength, μ_(o) is a constant equal to4π*10⁻³ Gauss * m/A, I is the current, and R is the radius of thecircle. Thus, in an exemplary embodiment where I is 0.2 mA and the loophas a radius of 30 nm, the resulting magnetic field is approximately 20Gauss. Due to the shape of the magnetic assist region 402, the netmagnetic field assists the change in magnetic orientation of the freelayer 112. Utilizing both the spin-torque transfer and the net magneticfield produced by the write current may reduce the switching current ofthe device 400 compared to that of a purely spin-torque transfer orpurely magnetic-field-write device. In an embodiment, a device 400 has athreshold STT (spin-torque transfer) current defined as a minimum writecurrent to reliably induce the intended field orientation in the freelayer 112 by spin-torque transfer alone. However, due in part to themagnetic field assist produced by the flow of the write current throughthe magnetic assist region 402, the switching current used to reliablyinduce the intended field orientation in the free layer 112 is lowerthan the threshold STT current. For example, the switching current maybe approximately 20% lower than the threshold STT current, and in someembodiments, the switching current is lower still.

The result is that in many embodiments, magnetic tunnel junction devicesthat incorporate an electrode with a magnetic assist region 402 such asthat of device 400 are more energy efficient and produce less heat. Thisconveys numerous benefits. For example, reduced energy and thermalrequirements may allow the MTJ devices 400 to be spaced closer and mayalso allow reductions in size and drive strength of supporting circuitryincluding the write current generator. In some embodiments, because themagnetic field produced by the write current need not be as strong asthe field of a magnetic-field-write device, there is a reduced risk ofaffecting an adjacent device. Additionally, the net magnetic fieldproduced by a magnetic assist region 402 is focused at the center of thecircle and diffuse outside the circumference. This further reduces thestrength of the magnetic field experienced by adjacent devices andfurther reduces the opportunity for an unintended write. Accordingly, insome embodiments, this alleviates related spacing concerns and allowssmaller inter-device spacing.

In the illustrated embodiment, the write current indicated by arrows 404induces a magnetic orientation in the free layer 112 in the directionindicated by arrow 204, that is, in an orientation substantiallyparallel to and in substantially the same direction as the magneticorientation of the pinned layer 108. This may be defined as a firstoperating condition. Likewise, a write current in the opposite directionmay induce a magnetic orientation in the free layer 112 in the oppositedirection, that is, in an orientation substantially parallel to but inthe substantially opposite direction of the magnetic orientation of thepinned layer 108. This may be defined as a second operating condition.The first and second operating conditions may correlate to first andsecond stored data values. For example, the first operating conditionand the associated low resistance state may correspond to a stored “0”binary value, and the second operating condition and the high resistancestate may correspond to a stored “1” binary value. In this way, thewrite current may store a value in the magnetic tunnel junction device400 via both spin-torque transfer and magnetic-field-write concurrently.In order to read the stored value, an electric potential may be appliedbetween the top electrode 114 and the bottom electrode 104, and thedevice 100 resistance may be measured.

The magnetic field orientations indicated by arrows 202 and 204 aremerely exemplary. One of skill in the art will recognize that in someembodiments, the fields of the pinned layer 108 and free layer 112 ofthe device 400 may be oriented differently, for example, substantiallyparallel to the interface of the pinned layer 108 and the barrier layer110. Other alignments both are contemplated and provided for. Thesealignments are equally suitable.

One of skill in the art will also recognize that the present disclosureencompasses alternate configurations of the magnetic assist region 402.For example, in the embodiment of FIG. 4, the magnetic assist region 402represents approximately 180° of a circle. In various other embodiments,the magnetic assist region 402 represents approximately 90°, 270°, and360° of a circle.

FIG. 5 is a perspective view of a spin-torque transfer magnetic tunneljunction (MTJ) device 500 incorporating a piecewise linear, partiallycircular, magnetic assist region 502 according to various aspects of thepresent disclosure. FIG. 5 has been simplified for clarity. For example,the magnetic tunnel junction device 500 may include one or moredielectric layers insulting the components of the device 500 andproviding structural support for the device 500 and associatedcomponents. As another example, the magnetic tunnel junction device 500may include one or more passivation layers and/or moisture blockinglayers. These have been omitted from FIG. 5 to reveal other elements ofthe device 500 more clearly. In many regards, the device 500 of FIG. 5is substantially similar to the magnetic tunnel junction device 100 ofFIG. 1 and the magnetic tunnel junction device 400 of FIG. 4. Forexample, device 500 may include a substrate 102, a top electrode 114, abottom electrode, a pinning layer 106, a pinned layer 108, a barrierlayer 110, and/or a free layer 112 substantially similar to those ofdevice 100.

In some embodiments, the top electrode 114 includes a magnetic assistregion 502 disposed above the free layer 112. The magnetic assist region502 is configured such that current flow through the region 502 producesa magnetic field that assists the spin-torque transfer of the current inaligning the magnetic orientation of the free layer 112. For example,the write current flowing in a first direction indicated by arrows 504induces, via spin-torque transfer, a net magnetic field in the freelayer 112 in the direction indicated by arrow 304 (e.g., an orientationsubstantially parallel to but in an substantially opposite direction ofthe magnetic orientation of the pinned layer 108). The same writecurrent flowing through the magnetic assist region 502 also produces amagnetic field as indicated by arrows 506. This magnetic field alsocontributes to induce, via a magnetic-field-write, a magnetic field inthe free layer 112 in the direction indicated by arrow 304 (e.g., anorientation substantially parallel to and substantially opposite themagnetic orientation of the pinned layer 108).

In contrast to the region 402 of FIG. 4, the magnetic assist region 502has a partially circular coil shape comprising piecewise linearsegments. In some design environments, linear segments are easier tomanufacture reliably than a circular or semi-circular shape.Accordingly, in some embodiments, the magnetic assist region 502 isformed from linear segments that make up the coil region having awinding orientation substantially perpendicular to the top surface ofthe free layer 112. In the illustrated embodiment, the designenvironment supports diagonal conductors, and thus, linear segments mayjoin at an angle of substantially 45°. Further embodiments supportadditional conductor orientations and additional segment anglesincluding substantially 30° and substantially 60°.

Similar to the embodiment of FIG. 4, the magnetic assist produced by theflow of the write current through the magnetic assist region 502 mayreduce the current threshold to alter the magnetic orientation of thefree layer 112 over that of a purely spin-torque transfer ormagnetic-field-write device. As a result, in many embodiments, themagnetic tunnel junction device 500 is more energy efficient andproduces less heat than designs utilizing spin-torque transfer ormagnetic-field-write alone.

FIG. 6 is a perspective view of a spin-torque transfer magnetic tunneljunction device 600 incorporating a partially rectangular magneticassist region 602 according to various aspects of the presentdisclosure. FIG. 6 has been simplified for clarity. For example, themagnetic tunnel junction device 600 may include one or more dielectriclayers insulting the components of the device 600 and providingstructural support for the device 600 and associated components. Asanother example, the magnetic tunnel junction device 600 may include oneor more passivation layers and/or moisture blocking layers. These havebeen omitted from FIG. 5 to reveal other elements of the device 600 moreclearly. In many regards, the device 600 of FIG. 5 is substantiallysimilar to the magnetic tunnel junction device 100 of FIG. 1, themagnetic tunnel junction device 400 of FIG. 4, and the magnetic tunneljunction device 500 of FIG. 5. For example, device 600 may include asubstrate 102, a top electrode 114, a bottom electrode, a pinning layer106, a pinned layer 108, a barrier layer 110, and/or a free layer 112substantially similar to those of device 100.

In some embodiments, the top electrode 114 includes a magnetic assistregion 602 disposed above the free layer 112. The magnetic assist region602 is configured such that current flow through the region 602 producesa magnetic field that assists the spin-torque transfer of the current inaligning the magnetic orientation of the free layer 112. For example,the write current flowing in a first direction indicated by arrows 604induces, via spin-torque transfer, a magnetic field in the free layer112 in the direction indicated by arrow 204 (e.g., an orientationsubstantially parallel to and in substantially the same direction as themagnetic orientation 202 of the pinned layer 108). The same writecurrent flowing through the magnetic assist region 602 also produces amagnetic field as indicated by arrows 606. This magnetic field alsocontributes to induce, via a magnetic-field-write, a magnetic field inthe free layer 112 in the direction indicated by arrow 204 (e.g., anorientation substantially parallel to and in substantially the samedirection as the magnetic orientation of the pinned layer 108).

In contrast to the region 402 of FIG. 4, magnetic assist region 602 hasa partially rectangular coil shape having a winding orientationsubstantially perpendicular to the top surface of the free layer 112.This shape is particularly well suited to design environments that onlysupport linear conductor segments and that only support two orientationsof conductor, although it is suitable to other design environments aswell. Similar to the embodiment of FIG. 4, the magnetic assist producedby the flow of the write current through the magnetic assist region 602may reduce the current threshold to alter the magnetic orientation ofthe free layer 112 over that of a purely spin-torque transfer ormagnetic-field-write device. As a result, in many embodiments, themagnetic tunnel junction device 600 is more energy efficient andproduces less heat than designs utilizing spin-torque transfer ormagnetic-field-write alone.

Thus, the present invention provides a structure and method for amagnetic assist spin-torque-transfer magnetic tunnel junction device. Insome exemplary embodiments, a magnetic tunnel junction device isdisclosed. The device comprises: a first electrode; a pinned layerdisposed on the first electrode; a free layer disposed on the pinnedlayer; a barrier layer disposed between the pinned layer and the freelayer; and a second electrode electrically coupled to the free layer,wherein the second electrode includes a magnetic assist region. In onesuch embodiment, the magnetic assist region is configured to produce anet magnetic field when supplied with a write current, and the netmagnetic field is aligned to assist a spin-torque transfer of the writecurrent on the free layer. In another such embodiment, the net magneticfield is aligned to orient an internal magnetic field of the free layerin a first orientation, and a spin-torque transfer of the write currenton the free layer is aligned to orient the internal magnetic field ofthe free layer in the first orientation. In another such embodiment, thedevice further comprises a longitudinal device body that includes thepinned layer, the free layer, and the barrier layer, and the firstorientation is substantially parallel to the longitudinal device body.In another such embodiment, the magnetic assist region includes a coilregion having a winding orientation substantially perpendicular to a topsurface of the free layer. In a further such embodiment, the coil regionincludes a partially circular region. In another such embodiment, thedevice further comprises a longitudinal device body that includes thepinned layer, the free layer, and the barrier layer, and the magneticassist region is substantially perpendicular to the longitudinal devicebody. In another such embodiment, the partially circular region ispiecewise linear. In a further such embodiment, the coil region includesa partially rectangular region.

In some exemplary embodiments, a magnetic tunnel junction device isdisclosed, the device comprising: a bottom electrode; a pinned layerdisposed on the bottom electrode; a barrier layer disposed on the pinnedlayer; a free layer disposed on the barrier layer; and a top electrodedisposed on and electrically coupled to the free layer, wherein the topelectrode is configured to produce a net magnetic field when suppliedwith a write current, wherein the net magnetic field is aligned toinduce a magnetic orientation within the free layer, and wherein aspin-torque of the write current is aligned to induce the magneticorientation within the free layer. In one such embodiment, the netmagnetic field is configured such that a switching current of the deviceis less than a threshold write current for a spin-torque transfer writeof the device. In another such embodiment, the device further comprisesa longitudinal device body that includes the pinned layer, the barrierlayer, and the free layer, and the magnetic orientation is substantiallyparallel to the longitudinal device body. In a further such embodiment,the top electrode includes a coil region having a winding orientationsubstantially perpendicular to a top surface of the free layer. Inanother such embodiment, the device further comprises a longitudinaldevice body that includes the pinned layer, the barrier layer, and thefree layer, and wherein the coil region is substantially perpendicularto the longitudinal device body. In one such embodiment, the coil regionincludes a piecewise linear partially circular region. In another suchembodiment, the top electrode includes a partially rectangular region.In a further such embodiment, the magnetic orientation is parallel to aninternal magnetic field orientation of the pinned layer.

In some exemplary embodiments, a method of writing to a magnetic tunneljunction device is disclosed. The method includes providing a writecurrent to a free layer of the magnetic tunnel junction device via anelectrode electrically coupled to the device, wherein a flow of thewrite current through the electrode produces a net electromagnetic fieldaligned to induce a magnetic orientation in the free layer, and whereinthe write current further induces the magnetic orientation in the freelayer via spin-torque transfer. In one such embodiment, the magneticorientation is substantially parallel to a device body of the magnetictunnel junction device. In another such embodiment, the magneticorientation is substantially parallel to and in substantially the samedirection as a magnetic orientation of a pinned layer of the magnetictunnel junction device. In a further such embodiment, the first magneticorientation is substantially parallel to and in a substantially oppositedirection of a magnetic orientation of a pinned layer of the magnetictunnel junction device.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A magnetic tunnel junction device comprising: afirst electrode; a pinned layer disposed on the first electrode; a freelayer disposed on the pinned layer; a barrier layer disposed between thepinned layer and the free layer; and a second electrode electricallycoupled to the free layer, wherein the second electrode includes amagnetic assist region.
 2. The device of claim 1, wherein the magneticassist region is configured to produce a net magnetic field whensupplied with a write current, and wherein the net magnetic field isaligned to assist a spin-torque transfer of the write current on thefree layer.
 3. The device of claim 1, wherein the net magnetic field isaligned to orient an internal magnetic field of the free layer in afirst orientation, and wherein a spin-torque transfer of the writecurrent on the free layer is aligned to orient the internal magneticfield of the free layer in the first orientation.
 4. The device of claim3, the device further comprising a longitudinal device body thatincludes the pinned layer, the free layer, and the barrier layer,wherein the first orientation is substantially parallel to thelongitudinal device body.
 5. The device of claim 1, wherein the magneticassist region includes a coil region having a winding orientationsubstantially perpendicular to a top surface of the free layer.
 6. Thedevice of claim 5, wherein the coil region includes a partially circularregion.
 7. The device of claim 6, wherein the partially circular regionis piecewise linear.
 8. The device of claim 5, wherein the coil regionincludes a partially rectangular region.
 9. A magnetic tunnel junctiondevice comprising: a bottom electrode; a pinned layer disposed on thebottom electrode; a barrier layer disposed on the pinned layer; a freelayer disposed on the barrier layer; and a top electrode disposed on andelectrically coupled to the free layer, wherein the top electrode isconfigured to produce a net magnetic field when supplied with a writecurrent, wherein the net magnetic field is aligned to induce a magneticorientation within the free layer, and wherein a spin-torque of thewrite current is aligned to induce the magnetic orientation within thefree layer.
 10. The device of claim 9, wherein the net magnetic field isconfigured such that a switching current of the device is less than athreshold write current for a spin-torque transfer write of the device.11. The device of claim 9, the device further comprising a longitudinaldevice body that includes the pinned layer, the barrier layer, and thefree layer, wherein the magnetic orientation is substantially parallelto the longitudinal device body.
 12. The device of claim 9, wherein thetop electrode includes a coil region having a winding orientationsubstantially perpendicular to a top surface of the free layer.
 13. Thedevice of claim 12, the device further comprising a longitudinal devicebody that includes the pinned layer, the barrier layer, and the freelayer, and wherein the coil region is substantially perpendicular to thelongitudinal device body.
 14. The device of claim 12, wherein the coilregion includes a piecewise linear partially circular region.
 15. Thedevice of claim 9, wherein the top electrode includes a partiallyrectangular region.
 16. The device of claim 9, wherein the magneticorientation is parallel to an internal magnetic field orientation of thepinned layer.
 17. A method of writing to a magnetic tunnel junctiondevice, the method comprising: providing a write current to a free layerof the magnetic tunnel junction device via an electrode electricallycoupled to the device, wherein a flow of the write current through theelectrode produces a net electromagnetic field aligned to induce amagnetic orientation in the free layer, and wherein the write currentfurther induces the magnetic orientation in the free layer viaspin-torque transfer.
 18. The method of claim 17, wherein the magneticorientation is substantially parallel to a device body of the magnetictunnel junction device.
 19. The method of claim 17, wherein the magneticorientation is substantially parallel to and in substantially the samedirection as a magnetic orientation of a pinned layer of the magnetictunnel junction device.
 20. The method of claim 17, wherein the firstmagnetic orientation is substantially parallel to and in a substantiallyopposite direction of a magnetic orientation of a pinned layer of themagnetic tunnel junction device.